The present invention relates to an open-topped disk brake having means for retracting the pads together with the piston to prevent the pads from dragging the disk when the fluid pressure is released.
An open-topped disk brake has a caliper having a window across which pad pins extend. The pad pins are inserted loosely through pin holes formed in back plates of the friction pads to axially slidably hang the pads. Since tangential torque is borne by the caliper, no torque is applied to the pad pins. By removing the pad pins, the friction pads can be pulled out through the window without the need to dismount the caliper from the vehicle knuckle. Worn pads can thus be replaced easily.
Ordinary disk brakes have pistons slidably received in fluid pressure cylinders formed in the caliper. To brake the disk, the pads are pressed against the disk. In a disk brake with opposed pistons, fluid pressure is applied to the opposed pistons to press both pads against the disk with the respective pistons. In a floating type disk brake, fluid pressure is applied to a piston or pistons on one side to press one of the pads with the pistons and press the other pad with a known reaction mechanism against the disk. When the pressure is released, the pistons are forcibly retracted by piston seals having retractor function as well as sealing function.
When the pressure is released, if only the pistons retract with the pads kept in frictional contact with the disk, the pads will apply dragging force to the disk, causing brake squeaks, uneven wear of the pads and the disk or judder resulting from change in the thickness of the disk. Dragging also incurs waste of energy and abnormal wear of the pads. Conventional disk brakes have therefore means for forcibly retracting the pads together with the pistons when the brake pressure is released, to reliably separate the pads from the disk.
FIG. 9 shows one such means which is disclosed in Japanese patent publication 9-53668 filed by the applicant of this invention. In this arrangement, a thin plate or shim 111 is disposed between the friction pad and the pistons on each side. The friction pads 106 hang from pad pins extending across the window of the caliper. Each shim 111 has first claws 114 resiliently gripping the back plate 106a of each pad 106 by engaging its inner side, and third claws 112 resiliently engaged in grooves formed in the pistons near their openings. In order to prevent the shims 111 and back plates 106a from moving radially outwardly of the disk, each shim 111 is secured to the back plate 106a by clips 116 mounted on the pad pins.
FIG. 10 shows a different conventional arrangement in which the clips 116 are not used. In this arrangement, each shim 111 has second claws 113 resiliently gripping the portions of the back plates 106a extending beyond the torque bearing portions of the friction pad 106 so that the friction pad 106 can slide radially of the disk.
In order that the pads can retract together with the pistons, no unnecessary play is permissible in the axial direction of the pistons, while the pads have to be mounted so that they can be slid out through the window when the pad pins are removed. To meet both these requirements, clips 116 are used in the first-mentioned prior art. But this arrangement is economically undesirable because the clips add to the number of brake parts. In the latter conventional arrangement, in which the second claws 113 grip the portions of the back plates 106a extending beyond the torque bearing portions of the friction pad 106, the claws 113 will collide against the torque bearing portions of the caliper every time the brake is applied. The claws will thus be quickly worn and/or deformed to such an extent as to lose their function of holding the back plates 106a.
The shims disposed between the friction pads and the pistons also help suppress disk brake squeaks. To suppress brake squeaks, it is important not to conduct the movement of the pads during braking directly to the pistons. But in the above prior art, the first and second claws and the clips join the shims directly to the pads in such a manner that the pads and shims can scarcely move in a direction parallel to the sliding surfaces of the pads relative to each other. In such an arrangement, the shims can scarcely suppress brake squeaks.